Telephone switchboards with signal-producing means



I United States Patent 1 13,549,s17

[72] Inventor Cliilord Jack Peady [56] References Cited Hurstville, NewSouth Wales, Australia UNITED STATES PATENTS [2.11 Q J- 9 1 1,587,1256/1926 0. M. Leich 179/94 2% f ted g i 1970 3,037,087 5/1962 H. H.Abbott et a1 179/42 E z fg Telpho'ne Manufacturing Co (Australasia)1,665,231 4/1928 M. B. Stazak 179/42 Proprietary Limited 1,713,5645/1929 M. B. Stazak 179/42 Erskineville, New South Wales, AustraliaPrimary Examiner- Kathleen H. Clafty a corporation of New South WaleAssistant Examiner-Jan S. Black Australia Attorney-M1chael S. Striker[32] Priority June 8, 1967 [33] Australia [31 No. 22907/67 ABSTRACT: Atelephone switchboard of the kind including a third connecting circuitbetween each extension telephone [54] g gg T SIGNAL and the switchboard,the third circuit including a gravity 4 Cl i 2D in n switch, recallbutton and a supervisory lamp together with a 8 raw 8 relay controllinga call-trapping facility wherein the necessity [52] [1.8. CI. for theprovision of an additional relay in the normal [51 Int. Cl. l-l04m 5/04telephone circuit is avoided by providing an arrangement such [50] Fieldof Search that operation of the gravity switch produces a signaldifferent 51.5, 27CA, 94, 175.24, 56, 71, 27.02 from the signal producedby the operation of the recall button.

TO NORMAL EXCHANGE TELEPHONE CIRCUIT CALL m l'i' connsc TING CIRCUIT I.l' v i fi GRAVITY SWITCH CONTACTS neon BUTTON CGITACTS 1 TELEPHONEswrrcirnoxims wmr SIGNAL- PRODUCING MEANS The present invention relatesto improvements in telephone switchboards and more particularly totelephone switchboards including call-trapping facilities.

The invention will be describedin more detail with regard to thefollowing drawing in which:

FIG. 1 is a depiction of the prior art; and

FIG. 2 shows an embodiment of the invention.

There is shown in FIG. I a circuit arrangement which is at present usedin switchboards and in this it will be seen that a third wire c isprovided in addition to the two wires a and b normally connecting theswitchboard to each extension telephone, the wire being used to actuatethe supervisory lamp on the switchboard. The circuit includes gravityswitch contacts which close when the, telephone receiver is replaced andcomplete the circuit of the supervisory lamp which glows to indicate thetermination of a call. The same supervisory lamp may also be energizedby means of the recall button con.- tacts which are operable by means ofa button on the extension telephone. This enables the caller to attractthe attention of the operator when a call is in progress.

In order to actuate a call-trapping facility CTR an additional relay CTis provided which controls a circuit which is not shown as its functionis not connected with the present invention. In the normal condition,that is to say, when a call is not being made, the relay CT isenergized. As the clearing signal given by the gravity switch contactsis identical with the signal given by the call button contacts, thissignal cannot be used for controlling relay CT and it is necessary toprovide an additional relay SA in wire b todete'ct the off-hookcondition. As SA responds to impulses from the telephone dial anauxiliary slow releasing relay SB is provided which is controlled by therelay SA and operates steadily while the extension telephone receiver isoff-hook and is not affected by the operation of the recall button.RelayCT is released when contacts 881 open. When the extension receiveris replaced relays SA and SB release and relay CTis reenergized toactuate a call-trapping facility.

As can be seen this arrangement is relatively complex and the necessityfor including the relay SA in the wire 12 presents design problems.

The object of the. present invention is to provide a more economicaldesign-by the elimination of the relay SA and its associated relay SB.

The invention consists in the provision, in a telephone switchboardincluding a third connecting circuit between each extension telephoneand the switchboard, the third circuit ineluding gravity switchcontacts, recall button contacts, a su pervisory lamp or other visibleor audible warning device and a relay controlling the call-trappingfacility CTR, of circuit means whereby operation of. the gravity switchcontacts produces a signal different from "the signal produced by theoperation of the recall button contacts and further circuit meanswhereby the supervisory lamp or other visible or audible warning deviceis caused-to operate on receipt of a signal either from the gravityswitch contacts or the recall button contacts whereas the relay isoperated to render the calltrapping facility inoperativeonly on receiptof a signal from the gravity switch contacts.

In order that the nature of the invention may be better understood acircuit embodying a preferred form thereof is shown in FIG. 2.

In the circuit of FIG. 2 it will-be seen that relay SA is omitted fromwire b altogether. Gravity switch contacts are included in wire c inseries with a resistor R3, the gravity switch contacts being arranged toclose when the receiver is lifted and in so doing connect earth viaresistor R3 to wire 0. In the normal or rest state of the circuit therelay CT is operated via the circuit including transistor TR yandresistor R1. When the receiver is lifted and earth is connected to thewire c via resistor R3, transistor TR is switched on causing transistorTR to be switched off and relay CT to release for the duration of thecall. Contacts CTl which are shown in the FIG. in the position occupiedwhen CT is deenergized connect the supervisory lamp to the'wire c butthe presence of R3 limits the current through the lamp so that it doesnot glow. If, however, the

recall button contacts are operated the wire 0 is connected directly toearth and the lamp glows while the button is pressed. It will be seenthat in this way a distinction is made between the signal produced bythe gravity switch contacts and the signal produced by the recall buttoncontacts by virtue of the presence of the resistor R3.

When the extension telephone receiver is replaced at the end of a call,earth via resistor R3 is disconnected from wire 0 and relay CTreoperates and the supervisory lamp is energized via contacts CT 1 andthe connecting circuit contacts until the operator disconnects theextension from the switchboard.

The essential feature of the-circuit which enables the relay SA to bedispensed which is the fact that a distinction is made between thesignal arriving at A produced by the gravity switch contacts and thesignal produced by the recall button contacts. Once this feature isintroduced into the circuit a variety of different circuit arrangementsmay be used for controlling the supervisory lamp or other visible oraudible warning device and the relay CT. The circuit given above ispreferred in that it is relatively simple and inexpensive to concircuitbetween each struct but other circuits skilled in the art.

lclaim: 1. A telephone switchboard including a third connectingextension telephone and the switchboard, the third circuit includinggravity switch contacts, recall button contacts, a supervisory lamp orother visible oraudible warning device and a relay controlling acalltrapping facility, wherein there is provided circuit means wherebyoperation of the gravity switch contacts produces a signal differentfrom the signal produced by the operation of the recall button contactsand further circuit means whereby the supervisory lamp or other visibleor audible warning device is caused to operate onreceipt of a signaleither from the gravity switch contacts or the recall button contactsmay be readily devised by those whereas the relay is operated to rendersaid call trapping facility inoperative only on receipt of a signal fromthe gravity switch contacts.

2. A telephone switchboard as claimed in claim 1 wherein closing of thegravity switch contacts is effected by the receiver of an extension andconnects the third connecting circuit to earth via a resistor whereinclosing of the recall button contacts connects the third connectingcircuit directly to earth. 7

3. A telephone switchboard as claimed in claim 2 wherein the said relayoperates contacts whereby the supervisory lamp or other warning deviceis connected to the third connecting circuit when the relay isdeenergized and to earth when it is energized 4. A telephone switchboardas claimed in claim 3 wherein the said relay is controlled by atransistor which is arranged to be switched on or off when the gravityswitch contacts are open or closed respectively.

